1. Field of the Invention
The present invention relates to a rotary encoder including a housing having a bottom wall provided with at least one opening, and a cover for closing the opening.
2. Description of the Prior Art
Rotary encoders are generally used for measuring the rotational movement of a rotatable body, in particular, a shaft, over one or several revolutions. The data characterizing the rotational movement of the rotatable body can be acquired incrementally or absolutely. When the rotary encoders are associated with racks and tooth gears or with threaded spindles, they can be used for measuring the linear movement.
Actuation voltage is fed to a rotary encoder via a connection cable which also serves for transmitting the measurement signal to servo-electronics. The housings of conventional rotary encoders are provided with an opening through which the connection cable is inserted and is connected with suitable electrical connection means located in the housing.
European Patent EPO 776 065 BI discloses a rotary encoder with a pot-shaped, hollow cylindrical housing having an opening provided in its bottom and insuring access to a connection plug for the connection cable, to a strain-relief device for the cable, and to connection means which connects the encoder shaft with a to-be-measured rotatable body. The opening is closed with a cover which is hingidly connected with the housing and, for covering the opening, snaps behind a projection. The snap connection between the cover and the housing is particularly stressed when the rotary encoder is subjected to vibrations or when a strong tension load is applied to the connection cable.
A publication xe2x80x9cPositional Encoders for Electrical Drivesxe2x80x9d (July, 1997) of the firm Dr. Johannes Heidenhain GmbH, an assignee herein, discloses a rotary encoder with a stator coupling for mounting in motors. The encoder housing has a circular rear wall and a large-surface opening formed in the rear wall and providing access to connection means for connecting the encoder shaft with to-be-measured rotatable body and to electrical connector means of the encoder.
The opening is covered with a cover which is connected to the rear wall of the housing with a fastening screw provided in the region of the outer edge of the rear wall. The screw connection is subjected to a substantial load when the rotary encoder is subjected to vibrations.
An object of the present invention is to provide a rotary encoder which would insure a reliable and durable attachment of the cover to the housing.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing in the housing rear wall, an attachment region which encloses the wall center and the opening(s), which provide(s) access to the connection means that connects the encoder shaft with the to-be-measured body, and the electrical connector, and which has an attachment point at which the fastening element is rotatably supported for securing the cover to the housing wall.
Experiments have shown that providing an attachment region that encloses the center of the rear wall and at which the fastening element is rotatably supported, insures a vibration-free attachment of the cover to a circular housing wall.
The solution according to the present invention can also be advantageously used when there is provided, in the housing wall, an opening, which is located eccentrically with respect to the wall center or is located outside of the center and which should be covered by the cover. In this case, this opening is covered by a cover that is secured to the housing wall by a fastening element centrally supported on the housing wall.
Behind at least one opening in the housing wall, an electrical connection element of the encoder is arranged. The connection element is accessible through the opening behind which it is arranged and therefore, can be connected with a mating connection element of the connection cable at least partially located outside of the housing.
Behind an opening in the housing wall, connection means or a connection element for connecting the encoder shaft with a code disc supported thereon with a to-be-measured body is located, which permits to actuate this connection element from outside of the housing.
In accordance with one embodiment of the present invention, the electrical connection element and the connection element for connecting the encoder shaft with to-be-measured body are associated with two separate openings which are formed in the housing wall and are closed by the same cover. In this case, the opening associated with the electrical connection element is located preferably outside of the housing wall center, with the opening associated with connection element being centrally located in the housing wall.
In accordance with another embodiment of the present invention, both the electrical connection element and the connection element for connecting the encoder shaft with a to-be-measured member are associated with one and the same opening formed in the housing wall and covered by the cover.
When a circular opening centrally located in the housing wall is associated with the connection element for connecting the encoder shaft with a to-be-measured body, this circular opening can also be used as an attachment point for securing the cover to the housing wall. To this end, the housing wall is formed with a punched-out hollow cylindrical section concentric with the circular opening. The hollow cylindrical section forms an attachment element which provides for securing the cover to the housing wall. The hollow cylindrical section can be provided, e.g., with an inner or outer thread.
Such a double function of a centrally located, circular opening, (namely, providing access to the shaft connection element, on one hand, and serving as an attachment point, on the other hand) is also then possible when it is formed not as a separate opening but is adjoined by a further, located off-center, opening that provides, e.g., access to the electrical connection element of the encoder. In this case, the centrally located, circular opening and the further opening, which is located outside of the housing wall center, form two sections of a common opening arranged eccentrically with respect to the housing wall center. In this case, it is important that the centrally located, circular opening be provided over an angle of more than 180xc2x0 with a thread or other fastening means, e.g., a bayonet connection cooperating with a mating element rotatable with respect to the axis of the centrally located, circular section of the common opening.
As in the conventional rotary encoders, in the inventive rotary encoder, there is provided a strain-relief device which is covered by the cover and becomes accessible upon the cover being removed.
In accordance with the present invention, the strain-relief device includes a receptacle provided in the housing wall for clampingly receiving a section of the connection cable.
According to one embodiment of the present invention, the receptacle is formed as a recess in which a section of the connection cable formlockingly engages.
In addition, the cover itself can be provided, at its side facing the housing wall, with a formation for receiving a section of the connection cable.
The section of the connection cable, which is received in the strain-relief device, has an electrically conductive sleeve, in particular a crimp sleeve, that provides an electrical connection between the sheath of the connection cable and the housing wall which preferably is formed of an electrically conductive material.
For securing the cover to the housing wall, there can be provided a fastening element separately from the cover, e.g., a screw. However, preferably, the fastening element is retained on the cover without a possibility of being lost. The fastening element can be rotatably held in a corresponding opening, e.g., by a retaining ring which prevents axial displacement of the fastening element from the cover.
As it has already been mentioned above, instead of a threaded connection, a bayonet connection can be used for securing the cover to the housing wall. With the bayonet connection as with the threaded connection, the fastening element is rotated relative to the housing wall at a corresponding attachment point to provide connection between the fastening element and the attachment point, whereby the cover is secured to the housing wall.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.